The openresty mysql driver is in pure lua. It has a very efficient socket/pooling mechanism, using sockets from nginx.
And http://leafo.net/lapis/ is missing again.
If you want to improve even further on the lua drivers, LuaJIT FFI is probably the right answer.
That's interesting..
>LuaJIT FFI is probably the right answer
Do you mean calling nginx internal functions (DB driver or location capture, like ngx_eval module does in that case) via FFI (I doubt if that is safe in any way) or just use libpq from LuaJIT directly?
There's some work being done by openresty author w.r.t. ffi for openresty itself, it might yield interesting results. And yes, I think both the option you listed are viable. But the lua drivers already perform very well.